The present invention relates to a semiconductor unit that includes a means for detecting a temperature of a semiconductor chip mounted on a circuit pattern of a ceramic substrate.
In semiconductor units, a temperature of the semiconductor unit is detected by a temperature detector to prevent damage on a semiconductor chip due to an excessive temperature rise caused by driving the semiconductor chip. In a semiconductor unit disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2002-76236, when such temperature rise is detected, the drive of the semiconductor chip is shut down. In the semiconductor unit disclosed in the reference No. 2002-76236, as shown in FIG. 7, semiconductor chips 53 are mounted on one of circuit patterns 52 formed on a ceramic substrate 51. One of the terminals of a thermistor 54 is soldered to the circuit pattern 52 on which the semiconductor chips 53 are mounted. The other terminal of the thermistor 54 is soldered to the different circuit pattern 52.
In a semiconductor chip incorporating a temperature sensor, a temperature of the semiconductor chip can be directly detected. In addition, as shown in FIG. 8, a temperature of semiconductor chips 63 mounted on a ceramic substrate 61 can be detected also by an external thermistor 66. The thermistor 66 is mounted on a metal base 65 by a screw 67. The ceramic substrate 61 has a circuit pattern 62 formed on the upper surface of a ceramic plate 69. Each of the semiconductor chips 63 is mounted on the circuit pattern 62 by solder H. The ceramic substrate 61 has a metal plate 68 bonded to the lower surface of the ceramic plate 69 and mounted on the metal base 65 by solder H.
In the semiconductor unit as shown in FIG. 7, when the thermistor 54 is mounted on the ceramic substrate 51 by soldering, the thermistor 54 need to be located across the different circuit patterns 52, and the process of manufacturing the semiconductor unit becomes complicated, accordingly. In addition, since one of the terminals of the thermistor 54 is soldered to the circuit pattern 52 on which the semiconductor chip 53 is mounted, the thermistor 54 is affected by noise generated by the switching operation of the semiconductor chips 53.
Also when the temperature sensor is incorporated in the semiconductor chip, the temperature sensor is affected by noise generated due to the switching operation of the semiconductor chip. Therefore, though the temperature sensor is located close to the semiconductor chip, a temperature of the semiconductor chip cannot be detected accurately. Additionally, in semiconductor units having a plurality of identical semiconductor chips, a temperature is generally detected at not all the semiconductor chips, but only at one semiconductor chip and, therefore, a space for connecting the temperature sensor in the other semiconductor chips of which temperature are not detected becomes useless. Furthermore, in the case of parallel-connected semiconductor chips used in an inverter so that a large amount of current flows through each arm, temperatures of all the semiconductor chips in each arm need not to be detected. However, the size of the semiconductor chip incorporating the temperature sensor is large, resulting in enlargement of the entire size of the semiconductor unit.
In the semiconductor unit as shown in FIG. 8, when the thermistor 66 is mounted to the metal base 65 by the screw 67, heat generated in the semiconductor chip 63 is transferred through the solder H, the circuit pattern 62, the ceramic plate 69, the metal plate 68, the solder H and the metal base 65 to the thermistor 66. In such a case, since heat transfer resistance of a path from the semiconductor chip 63 to the thermistor 66 is large, the time when the thermistor 66 detects actual temperature of the semiconductor chip 63 may be delayed, or the thermistor 66 may fail to detect peak temperature of the semiconductor chip 63.
The present invention is directed to providing a semiconductor unit that allows more accurate detection of a temperature of a semiconductor chip mounted on a circuit pattern of a ceramic substrate without enlarging the size of the unit.